Cellular Control

Question 1

Define mutation

Answer 1

A change in the genetic material which may affect the phenotype of the organism

Question 2

Define point mutation

Answer 2

Changes one base in the triplet codon-may or may not have damaging effects

Question 3

Define substitution

Answer 3

A mutation where one or more nucleotides are substituted for another in a DNA strand

Question 4

Define deletion

Answer 4

Mutations where one or more nucleotides are deleted and lost from the DNA strand

Question 5

Define insertion

Answer 5

A mutation where one or more extra nucleotides are inserted into a DNA strand

Question 6

Define frame shift

Answer 6

1. The deletion or insertion of a nucleotide or nucleotides leads to a frame-shift mutation.
2. It shifts the reading frame of the sequence of bases, it will change every successive codon from the point of mutation

Question 7

Define silent mutation

Answer 7

A mutation that occurs in the part of a gene that does not code for a protein therefore it will not affect the phenotype.

Question 8

Define nonsense mutation

Answer 8

1. Result in a codon becoming a stop codon instead of coding for an amino acids.
2. The result is a shortened protein being synthesised which is normally non-functional

Question 9

Define misense mutation

Answer 9

1. Result in the incorporation of an incorrect amino acid/acids into the primary structure when the protein is synthesised.
2. The mutation could be silent, beneficial or harmful

Question 10

Define gene mutation

Answer 10

Gene mutations occur in single genes or sections of DNA

Question 11

Define chromosome mutation

Answer 11

1. Chromosome mutations affect the whole chromosome or number of chromosomes within a cell.

Question 12

Explain why a change in the sequence of nucleotides of a gene can affect the function of the protein produced from that gene.

Answer 12

1. A change in a base sequence may change the amino acid the codon codes for.
2. This leads to changes in the primary structure of the protein.
3. But as it is degenerate it may mean the new codon still codes for the same amino acid so no change to protein.

Question 13

Describe how a mutation can have a neutral effect, a harmful effect or a beneficial effect, and give an example of each

Answer 13

1. Neutral- no effect on the phenotype of an organism because normally functioning proteins are still synthesised
2. Harmful- the phenotype of an organism is affected in a negative way because proteins are no longer synthesised or proteins synthesised are no longer functional.- interfere with essential processes.
3. Beneficial- proteins is synthesised so it has new and useful characteristics in the phenotype.- e.g immunity to HIV from proteins in cell surface membrane

Question 14

State the 3 types of mutagen and give an example of each

Answer 14

1. Physical- ionizing radiation such as x-rays- break one or both DNA strands
2. Chemical- Deaminating agents- chemically alter bases in DNA
3. Biological agents
   a) Alkylating agents- methyl or ethyl groups are attached to bases- results in incorrect base pairing
   b) Base analogs- incorporated into DNA in place of the usual bases in replication
   c) Viruses- viral DNA may insert itself into a genome

Question 15

Name and describe the 4 types of chromosome mutation

Answer 15

1. Deletion- a section of chromosomes breaks off and is lost within the cell
2. Duplication- sections get duplicated on a chromosomes
3. Translocation- a section of one chromosome breaks off and joins another non-homologous chromosome
4. Inversion- a section of chromosome breaks off, is reversed and then joins back onto the chromosome

Question 16

Describe and explain the possible effects of a substitution mutation.

Answer 16

1. It changes the codon so if the new codon codes for a different amino acid this will leas to change in proteins
2. But it may not as it is degenerate

Question 17

Describe and explain the possible effects of insertion or deletion mutations

Answer 17

1. The insertion or deletion of a nucleotide or nucleotides leads to a frameshift mutation.
2. It changes every successive codon from the point of mutation

Question 18

Define gene expression

Answer 18

Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product. - often proteins

Question 19

Define epigenetics

Answer 19

External control of genetic regulation

Question 20

Name and describe the four levels at which genes (or proteins) are regulated

Answer 20

1. Transcriptional- genes can be turned on or off
2. Post-transcriptional- mRNA can be modified which regulates translation and types of proteins produced
3. Translational- translation can be stopped or started
4. Post-translational- proteins can be modified after synthesis which changes their functions

Question 21

Define chromatin

Answer 21

Uncondensed DNA in a complex with histones

Question 22

Define heterochromatin

Answer 22

Tightly packed DNA causing chromosomes to be visible during cell division

Question 23

Define euchromatin

Answer 23

Loosely packed DNA present during interphase

Question 24

Describe how chromatin remodelling allows the expression of some genes but not others.

Answer 24

1. The transcription of genes is not possible when DNA is tightly wound because RNA polymerase cannot access the genes.
2. The genes in euchromatin can be freely transcribed
3. Proteins synthesis does not occur during cell division as it is heterochromatin but it does during interphase between cell divisions as it is euchromatin
4. This is a simple form of regulation that ensures the proteins necessary for cell division are synthesised in time.
5. It also prevents the complex and energy-consuming process of protein synthesis form occurring when cells are actually dividing.

Question 25

Describe how histone modification can affect gene expression

Answer 25

1. DNA coils around histones because they are positively charged and DNA is negatively charged 2. Histones can be modified to increase or decrease the degree of packing (or condensation) 3. The addition of acetyl groups (acetylation) or phosphate groups (phosphorylation) reduces the positive charge on the histones and this causes DNA to coil less tightly allowing certain genes to be transcribed. 4. The addition of methyl groups (methylation) makes histones more hydrophobic so they bind more tightly to each other causing DNA to coil more tightly and preventing transcription of genes.

Question 26

Define the term “operon"

Answer 26

Group of genes expressed together- they are under control of the same regulatory mechanism

Question 27

Draw and label a diagram to show the lac operon and its associated regulatory gene.

Answer 27

1. Regulatory gene- lacIgene which makes repressor protein (not part of operon) 2. Promoter- site of RNA polymerase binding 3. Operator- allows the genes to be turned on or off, depending on binding of a repressor protein 4. Structural genes needed to metabolise lactose - protein 1- lac Z - protein 2-lac Y - protein 3- lac A

Question 28

Define the term “structural gene”

Answer 28

Genes that code for structural proteins or enzymes not involved in DNA regulation

Question 29

Name the proteins produced from the structural genes in the lac operon.

Answer 29

1. Protein 1- lac Z- Beta galactosidase- breaks down lactose 2. Protein 2- lac Y- Lactose permease- brings lactose into cell 3. Protein 3- lac A- Transacetylase- unknown function

Question 30

Describe the roles of the regulatory gene, the structural genes the lac operon for the metabolism of lactose.

Answer 30

1. lac I is a regulatory gene- located near to the operon and codes for a repressor protein that prevents the transcription of the structural genes in the absence of lactose 2. Structural genes- code for three enzymes which are transcribed onto a single long molecule of mRNA but are translated into the 3 enzymes

Question 31

When is lactose used as a respiratory substrate for Escherichia coli

Answer 31

1. Glucose is easier to metabolise and is the preferred respiratory substrate. 2. If glucose is in short supply, lactose can be used as a respiratory substrate. 3. Different enzymes are needed to metabolise lactose

Question 32

Explain how the lac operon works when lactose is absent from the growth medium

Answer 32

1. The repressor protein is constantly being produced and binds to an area called the operator 2. The binding of this protein prevents RNA polymerase binding to DNA and beginning transcription. - down regulation 3. The section of DNA that is the binding site for the RNA polymerase is called the promoter

Question 33

Explain how the lac operon works when lactose is present in the growth medium

Answer 33

1. When lactose is present, it binds to the repressor protein causing it to change shape so it can no longer bind to the operator. 2. As a result RNA polymerase can bind to the promoter, the 3 structural genes are transcribed and the enzymes are synthesised.

Question 34

Describe the role of cAMP in control of the lac operon.

Answer 34

1. The binding of RNA polymerase still only results in a relatively slow rate of transcription that needs t be increased or up-regulated to produce the required quantity of enzymes to metabolise lactose efficiently 2. This is achieved by the binding of another protein, cAMP receptor protein (CRP)- only possible when CRP is bound to cAMP 3. The transport of glucose into an E.Coli cell decreases the levels of cAMP, reducing the transcription of the genes responsible for the metabolism of lactose. 4. If both glucose and lactose are present then it will still be glucose that is metabolised.

Question 35

Define intron

Answer 35

Regions of non-coding DNA or RNA

Question 36

Define exons

Answer 36

Regions of coding DNA or RNA

Question 37

Define pre mRNA

Answer 37

The mRNA transcribed from the DNA before any post-transcriptional regulation to remove introns

Question 38

Define mature mRNA

Answer 38

mRNA after the removal of introns and any other post-transcriptional changes

Question 39

Define RNA processing

Answer 39

RNA processing refers to any modification made to RNA between its transcription and its final function in the cell.

Question 40

Define RNA editing

Answer 40

1. When the nucleotide sequence of mRNA molecules are changed through base addition, deletion or substitution. 2. Same effect as point mutations and can result in the synthesis of different proteins- increases the range of proteins that can be produced from a single mRNA molecule or gene 3. A type of RNA processing

Question 41

Describe how pre-mRNA is modified to produce mature mRNA, where this occurs and the benefit of this modification process.

Answer 41

Post-transcriptional/ pre-translational control 1. A cap (modified nucleotide) is added to the 5' end and a tail (a long chain of adenine nucleotides) is added to the 3' end. 2. These both help to stabilise mRNA and delay degradation in the cytoplasm 3. The cap also aids binding of mRNA to ribosomes. 4. Splicing occurs where the RNA is cut at specific points- the introns are removed and the exons are joined together. Both processes occur in the nucleus.

Question 42

Describe 3 mechanisms that can regulate protein synthesis at the translational level.

Answer 42

1. Degradation of mRNA- the more resistant the molecule the longer it will last in the cytoplasm- greater quantity of protein synthesised. 2. Binding of inhibitory proteins to mRNA- prevents it binding to ribosomes and the synthesis of proteins 3. Activation of initiation factors which aid the binding of mRNA to ribosomes

Question 43

Describe the role of protein kinases in regulation of gene expression or protein activity

Answer 43

1. Enzymes that catalyse the addition of phosphate groups to proteins 2. The addition of a phosphate group changes the primary structure and so the function of a protein 3. Many enzymes are activated by phosphorylation. 4. Protein kinases are therefore important regulators of cell activity 5. Protein kinases are themselves often activated by the secondary messenger cAMP.

Question 44

Describe 4 ways in which proteins can be modified to provide post-translational control.

Answer 44

Involves modifications to the proteins that have been synthesised. 1. Addition of non-protein groups such as carbohydrate chains, lipids or phosphates 2. Modifying amino acids and the formation of bonds such as disulfide bridges 3. Folding or shortening of proteins 4. Modification by cAMP- e.g in lac Operon cAMP binds to cAMP receptor protein

Question 45

Define body plan

Answer 45

The basic shape of members of an animal phylum; the general structure each individual organism assumes as it develops.

Question 46

Define morphogenesis

Answer 46

The regulation of the pattern of anatomical development

Question 47

Define homeobox gene

Answer 47

Genes responsible for the development of body plans. | Homeotic/regulatory gene contains the homeobox sequence that codes for the homeodomain .

Question 48

Define homeodomain

Answer 48

A conserved motif of 60 amino acids found in all homeobox proteins. It is the part of the protein that binds to DNA allowing the protein to act as a transcriptional regulator

Question 49

Define Hox genes

Answer 49

A group of homeobox genes that are only present in animals

Question 50

Name the 3 kingdoms which all have very similar homeobox genes.

Answer 50

Plants, animals and fungi

Question 51

Define the term “highly conserved”.

Answer 51

Highly conserved- very similar

Question 52

Describe the role of Hox genes in controlling the body plan of animals

Answer 52

1. They are responsible for the correct positioning of body parts 2. In animals the Hox genes are found in gene clusters- mammals have 4 clusters on different chromosomes 3. The order in which the genes appear along the chromosomes is the order in which their effects are expressed in the organism 4. Humans have 39 Hox genes in total that are believed to have originated from one from one ancient homeobox gene

Question 53

Describe the layout of living organisms

Answer 53

1. Body plans are usually represented as cross-sections through the organisms showing the fundamental arrangement of tissue layers 2. Diploblastic animals- 2 primary tissue layers 3. Triploblastic animals- 3 primary tissue layers 4. All animals are segmented- the segments have multiplied over time and are specialised to perform different functions 5. Hox genes in the head control the development of mouth-parts 6. Hox genes in the thorax control development of wings, limbs or ribs 7. The individual vertebrae and associated structures have all developed from segments in the embryo called somites which are directed by Hox genes to develop in a particular way depending on their position in the sequence

Question 54

What are the different types of symmetry in animal body shape

Answer 54

1. Radial symmetry- seen in diploblastic animals- no right or left sides only a top or bottom e.g. jellyfish 2. Bilateral symmetry- most animals- have both right and left sides and a head and a tail rather than just a top and bottom 3. Asymmetry- sponges- no lines of symmetry

Question 55

Define apoptosis

Answer 55

Programmed and controlled cell death important in controlling the body form and in the removal of damaged or diseased cells

Question 56

Outline the process of apoptosis.

Answer 56

1. Similar to sculptor and wood 2. The shape is revealed as material is removed bit by bit- removes unwanted cells and tissues to shape different body parts 3. Cells undergoing apoptosis can also release chemical signals which stimulate mitosis and cell proliferation leading to the remodelling of tissues 4. Regulated by Hox genes

Question 57

Describe the steps in the process of apoptosis

Answer 57

1. Enzymes inside the cell break down important cell components such as proteins in the cytoplasm and DNA in the nucleus 2. The cell's contents are broken down it begins to shrink and the nucleus condenses and the cell forms blebs 3. Proteins start to breakdown the cell compartments and enzymes break down the nucleus 4. The DNA fragments 3. The cell fragments are engulfed by phagocytes and digested.

Question 58

Explain how apoptosis is controlled

Answer 58

1. Hox genes regulate apoptosis and mitosis 2. During development, genes that control apoptosis and genes that control mitosis are switched on or off in appropriate cells 3. This means some cells die, whilst some new cells are produced and the correct body plan develops

Question 59

Describe the role of mitosis and apoptosis in growth and development

Answer 59

1. Mitosis and differentiation create the bulk of body parts and then apoptosis refines the parts by removing unwanted structures

Question 60

Define the term “stress” in relation to homeostasis and describe the factors that may influence the rate of mitosis or apoptosis.

Answer 60

1. The expression of regulatory genes can be influenced by the environment, internal and external Stress can be defined as the condition produced when the homeostatic balance within an organism is upset 3. An internal stimulus could be DNA damage- if detected during cell cycle this can result in the expression of genes which cause the cycle to be paused and can even trigger apoptosis 4. An external stimulus-lack of nutrient availability- could result in gene expression that prevents cells from undergoing mitosis. Attack by pathogen leads to apoptosis.